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ABSTRACT
Ultimate screw withdrawal loads (USWLs) from panel face and edge of furnituregrade southern pine (Pinus spp.) and sweetgum (Liquidambar styraciflua L.) plywood were evaluated at five moisture contents (MCs). Both face and edge USWL decreased in general with increases in MC within the hygroscopic range. The effect of moisture on edge USWL was more pronounced than on face USWL. For each plywood, USWL from the panel face was significantly larger than the USWL value from the panel edge. At higher MC levels, edge screw-holding capacities deteriorated more rapidly than face screw-holding capacities. For plywood with comparable properties (e.g., panel thickness, bending stiffness and strength), wood species (pine vs. sweetgum) had an insignificant effect on USWL. Thus, sweetgum plywood is as good as pine plywood in screw-holding strength.
Interior-type plywood is widely used in construction of furniture and cabinets. The integrity of such construction is frequently dependent upon the connections between its components. For maximum strength and stability, each connection requires a design that is adapted to the fastener type and to the strength properties ofthe individual structural members.' Ultimate fastener withdrawal loads for plywood joints depend on fastener type (screw or nail), fastening direction (face or edge), panel moisture content (MC), and wood species used to manufacture the plywood. The ASTM standard2 specifies that screw withdrawal tests be conducted in both dry and soaked conditions for wood-based panels. However, for interior-type plywood used for furniture and cabinet manufacturing, plywood joints or constructions at complete watersoaked condition are rare. On the other hand, MC of the panel does fluctuate within the hygroscopic range depending on geographic location, season of the year, etc. This fluctuation in MC can significantly alter the screw-holding capacity of the panel and its structural integrity. Very little information exists, however, on the effects of moisture, fastening direction, and wood species on the ultimate screw withdrawal load (USWL) for furniture-grade plywood. The information is greatly needed for manufacturing, buying and selling plywood panels, and for better construction of plywood joints in furniture and cabinets.
The purpose of this study was to measure and quantify the influence of moisture, fastening direction, and wood species on USWL of interior-type plywood manufactured for furniture, cabinet, and millwork markets.
MATERIALS AND METHODS
Interior-type southern pine...